1. Field of the Invention
The present invention relates to a multi-media communication device for communicating multiple media such as image (dynamic or still picture image), voice, code and data (thereinafter simply referred to as data), in a combination thereof, via a digital network such as ISDN (Integrated Services Digital Network) between remote sites.
2. Related Background Art
Recently, communication services with the ISDN line have been put to practical use, and the AV (Audio Visual) services such as a television telephone or television conference system using the ISDN line are noted. For the AV services, the international standards have been defined by the CCITT (International Telegraph and Telephone Consultive Comittee), and its draft has been published. For example, the service rules, the protocol rules, and the multi-media multiplexing frame structure rules for AV services have been published as the CCITT recommendations or recommendation drafts H.221, H.242 and H.320. In H.221, the frame structure or exchange of terminal ability for the AV services on the B channel, having a transmission rate of 64 kbps to 1920 kbps, and further the encode allocation of BAS (Bitrate Allocation Signal), useful for the specification of communication mode, are defined. Also in H.242, the protocols for the ability exchange using the BAS between AV terminals and the communication mode changeover are defined, while in H.320, the outline of the overall AV services system is defined.
However, in conventional multi-media communication terminals, the communication path between terminals on initial and additional channels is set (CCITT recommendation I series), and then after the synchronization in the in-channel (B channel) has been established (CCITT recommendation H.221), a predetermined protocol (CCITT recommendation H.242) such as an exchange sequence of terminal ability using the BAS in the in-channel or a mode changeover sequence with the specification of communication mode is executed to perform the multi-media communication of voice, image and data, etc., between terminals.
However, it is out of the range of the rules that each terminal can change its own terminal ability depending on the situation, or what communication mode is to be used within a scope of exchanged ability.
The information transfer rate (communication rate) of each medium in the multi-media communication can be determined by specifying the audio encode method for the audio information, or for the data information, specifying the presence or absence of its use and the transfer rate to be used, in which the information transfer rate on the entire communication path (channel) set up, subtracted by the transfer rates of audio information and data information, becomes a transfer rate for the image information. Accordingly, the information of the transfer rate to be specified in notifying the partner of its own communication mode with the BAS is the audio encode method and the data transfer rate, in which for the image, the transfer rate is automatically set within the system.
However, in the above example, the operator needs the knowledge of the information transfer rate on the communication path and the information transfer rate for each of various types of audio encode methods,in order to know the transfer rate of image information, and further requires the operation for calculating the image transfer rate by taking into consideration the data transfer rate specified.
Also, each terminal can freely change its own terminal ability, depending on the situation, and further when the ability is exchanged in accordance with the CCITT recommendation H.242, which communication mode should be used within a scope of exchanged ability is not defined but can be freely set. For example, when the transfer rate ability is 2B in the exchanged ability, 1B or 2B can be used as the transfer rate mode, and when 2B is used as the transfer rate mode, the communication using a plurality of B channels is enabled. When the communication is performed using a plurality of channels, the additional channels are set on the B channel (in-channel) set by initiating a new call setting procedure, and then a procedure of mode changeover into a transfer rate mode corresponding to the number of additional channels set is executed.
However, in a conventional multi-media communication terminal in which a plurality of B channels as above described are usable, the operator must initiate a call setting or disconnection operating an operation unit such as a keyboard, in performing the call setting or disconnection for the additional channel, in which there was a problem that the operator was forced to perform troublesome operations.
That is, when the transfer rate mode is increased within a scope of transfer rate ability exchanged after the setting of initial channel (first channel), the operator is required to perform the new call setting procedure for setting the additional channels (second and subsequent channels) to change the transfer rate mode, while when the transfer rate mode is decreased, the operator is required to perform a call disconnection procedure for unused additional channels, resulting in a problem that the operator was subject to a burden of performing such a complex call control operation.